MainPageModel 的构造函数中的 App.Current.MainPage NullReferenceException [英] App.Current.MainPage NullReferenceException in Constructor of MainPageModel

问题描述

在加载MainPage 时，我正在从MainPageModel 的构造函数推送另一个页面.它在 MainPageModel 中抛出 NullReferenceException.这是我的代码

On the loading of MainPage, I am pushing another page from Constructor of MainPageModel. It throws NullReferenceException in MainPageModel. This is my code

MainPage 构造函数

MainPage constructor

public MainPage()
{
    InitializeComponent();
    Title = "MainPage";
    BindingContext = new MainPageViewModel(); 
}

MainPageModel 构造函数

MainPageModel constructor

public MainPageViewModel()
{
    App.Current.MainPage.Navigation.PushAsync(new HomePage()); //Exception
    //CommandMenu1 = new Command(async () => await NavigateNext());
}

我该如何解决这个问题?

How can I solve this issue?

推荐答案

可能发生的事情是这样的:

What probably happens is this:

public class App
{
    MainPage = new MainPage();
}

MainPage() 构造函数必须先完成，然后才能分配给 App 的 MainPage 属性.因此，在此之前尝试访问App.Current.MainPage，您将得到一个NullReferenceException.这意味着您必须找到另一种方法来实现您在此处尝试做的事情.

The MainPage() constructor has to be completed before it is assigned to the MainPage property of your App. Therefore, trying to access the App.Current.MainPage before then, you will get a NullReferenceException. This means you will have to find another way to achieve what you are trying to do here.

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